CLASS-7
CROSS PRODUCT RULE OF PROPORTION

CROSS PRODUCT PROPORTION

Suppose, w, x, y, and z are the 1^st, 2^nd, 3^rd, and 4^th terms of the proportion respectively then the equation would be  w : x =  y : z . The 1^st & 4^th terms are called EXTREMES and the 2^nd & 3^rd terms are called MEANS.

The term z is considered as a 4^th and also called the Fourth Proportional to w, x, y.

         1^st Term         3^rd Term             w              y

 So, ------------ = ------------  ;  --------  =  --------    

         2^nd Term         4^th Term             x              z

 If we multiply both the 1^st Term X 4^th Term = 3^rd Term X 2^nd Term ; so, wz = yx

 The above process is called the cross product rule. 

If four numbers w, x, y, & z are in proportion of which any three is known, we can know the remaining unknown number by using the fact that wz = yx .

  If four numbers are in proportion then

We can conclude that, the product of the EXTREMES = the product of the MEANS

 The above rule helps us to find any term of proportion if any three are known to us.